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28 Mar 2013

Volume 138, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 138, 124701 (2013); http://dx.doi.org/10.1063/1.4794685 (9 pages)

Luying Wang, Randall S. Dumont, and James M. Dickson
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back to top Theoretical Methods and Algorithms

Analytical energy gradient used in variational Born-Oppenheimer calculations with all-electron explicitly correlated Gaussian functions for molecules containing one π electron

Wei-Cheng Tung, Michele Pavanello, Keeper L. Sharkey, Nikita Kirnosov, and Ludwik Adamowicz

J. Chem. Phys. 138, 124101 (2013); http://dx.doi.org/10.1063/1.4795094 (11 pages)

Online Publication Date: 22 March 2013

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An algorithm for variational calculations of molecules with one π electron performed with all-electron explicitly correlated Gaussian (ECG) functions with floating centers is derived and implemented. The algorithm includes the analytic gradient of the Born-Oppenheimer electronic energy determined with respect to the ECG exponential parameters and the coordinates of the Gaussian centers. The availability of the gradient greatly accelerates the variational energy minimization. The algorithm is tested in calculations of four electronic excited states, c3Πu, C1Πu, i3Πg, and I1Πg, of the hydrogen molecule at a single internuclear distance specific to each state. With the use of the analytical energy gradient, the present calculations yield new, lowest-to-date, variational energy upper bounds for all four states.
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31.15.vj Electron correlation calculations for atoms and ions: excited states

Hyperfine interaction mechanism of magnetic field effects in sequential fluorophore and exciplex fluorescence

Dmitry V. Dodin, Anatoly I. Ivanov, and Anatoly I. Burshtein

J. Chem. Phys. 138, 124102 (2013); http://dx.doi.org/10.1063/1.4795576 (11 pages)

Online Publication Date: 22 March 2013

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The magnetic field effect on the fluorescence of the photoexcited electron acceptor, 1A*, and the exciplex, 1[D+δA−δ] formed at contact of 1A* with an electron donor 1D, is theoretically explored in the framework of Integral Encounter Theory. It is assumed that the excited fluorophore is equilibrated with the exciplex that reversibly dissociates into the radical-ion pair. The magnetic field sensitive stage is the spin conversion in the resulting geminate radical-ion pair, 1, 3[D+…A−] that proceeds due to hyperfine interaction. We confirm our earlier conclusion (obtained with a rate description of spin conversion) that in the model with a single nucleus spin 1/2 the magnitude of the Magnetic Field Effect (MFE) also vanishes in the opposite limits of low and high dielectric permittivity of the solvent. Moreover, it is shown that MFE being positive at small hyperfine interaction A, first increases with A but approaching the maximum starts to decrease and even changes the sign.
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33.50.Dq Fluorescence and phosphorescence spectra
82.20.Yn Solvent effects on reactivity
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
33.57.+c Magneto-optical and electro-optical spectra and effects
31.30.Gs Hyperfine interactions and isotope effects
31.70.Dk Environmental and solvent effects

Direct evaluation of the saddle splay modulus of a liquid-liquid interface using the classical mean field lattice model

F. A. M. Leermakers

J. Chem. Phys. 138, 124103 (2013); http://dx.doi.org/10.1063/1.4795607 (7 pages)

Online Publication Date: 22 March 2013

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We study the curvature dependence of the liquid-liquid (liquid-gas) interface using the well-known mean field lattice model to estimate its rigidity parameters. The Gaussian or saddle-splay modulus is found by evaluating the curvature energy of an interface onto which a saddle shape is imposed as this occurs in an Im3m cubic phase. The resulting values are consistent with those found by the classical indirect route, wherein the Gaussian bending modulus results from combining the curvature dependences of the interfacial tension in cylindrical and spherical geometries.
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68.03.Cd Surface tension and related phenomena
68.05.Cf Liquid-liquid interface structure: measurements and simulations
62.10.+s Mechanical properties of liquids

An optimized semiclassical approximation for vibrational response functions

Mallory Gerace and Roger F. Loring

J. Chem. Phys. 138, 124104 (2013); http://dx.doi.org/10.1063/1.4795941 (11 pages)

Online Publication Date: 25 March 2013

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The observables of multidimensional infrared spectroscopy may be calculated from nonlinear vibrational response functions. Fully quantum dynamical calculations of vibrational response functions are generally impractical, while completely classical calculations are qualitatively incorrect at long times. These challenges motivate the development of semiclassical approximations to quantum mechanics, which use classical mechanical information to reconstruct quantum effects. The mean-trajectory (MT) approximation is a semiclassical approach to quantum vibrational response functions employing classical trajectories linked by deterministic transitions representing the effects of the radiation-matter interaction. Previous application of the MT approximation to the third-order response function R(3)(t3, t2, t1) demonstrated that the method quantitatively describes the coherence dynamics of the t3 and t1 evolution times, but is qualitatively incorrect for the waiting-time t2 period. Here we develop an optimized version of the MT approximation by elucidating the connection between this semiclassical approach and the double-sided Feynman diagrams (2FD) that represent the quantum response. Establishing the direct connection between 2FD and semiclassical paths motivates a systematic derivation of an optimized MT approximation (OMT). The OMT uses classical mechanical inputs to accurately reproduce quantum dynamics associated with all three propagation times of the third-order vibrational response function.
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33.20.Tp Vibrational analysis
33.20.Ea Infrared spectra
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Lattice Boltzmann implementation of the three-dimensional Ben-Naim potential for water-like fluids

Nasrollah Moradi, Andreas Greiner, Francesco Rao, and Sauro Succi

J. Chem. Phys. 138, 124105 (2013); http://dx.doi.org/10.1063/1.4795008 (9 pages)

Online Publication Date: 26 March 2013

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We develop a three-dimensional lattice Boltzmann (LB) model accounting for directional interactions between water-like molecules, based on the so-called Ben-Naim (BN) potential [A. Ben-Naim, Molecular Theory of Water and Aqueous Solutions: Part I: Understanding Water (World Scientific Publishing Company, 2010); A. Ben-Naim, “Statistical mechanics of ‘waterlike’ particles in two dimensions. I. Physical model and application of the Percus-Yevick equation,” J. Chem. Phys. 54, 3682 (1971)]10.1063/1.1675414. The water-like molecules are represented by rigid tetrahedra, with two donors and two acceptors at the corners and interacting with neighboring tetrahedra, sitting on the nodes of a regular lattice. The tetrahedra are free to rotate about their centers under the drive of the torque arising from the interparticle potential. The orientations of the water molecules are evolved in time via an overdamped Langevin dynamics for the torque, which is solved by means of a quaternion technique. The resulting advection-diffusion-reaction equation for the quaternion components is solved by a LB method, acting as a dynamic minimizer for the global energy of the fluid. By adding thermal fluctuations to the torque equation, the model is shown to reproduce some microscopic features of real water, such as an average number of hydrogen bonds per molecules (HBs) between 3 and 4, in a qualitative agreement with microscopic water models. Albeit slower than a standard LB solver for ordinary fluids, the present scheme opens up potentially far-reaching scenarios for multiscale applications based on a coarse-grained representation of the water solvent.
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66.10.C- Diffusion and thermal diffusion
61.20.Ja Computer simulation of liquid structure

Complex-scaled equation-of-motion coupled-cluster method with single and double substitutions for autoionizing excited states: Theory, implementation, and examples

Ksenia B. Bravaya, Dmitry Zuev, Evgeny Epifanovsky, and Anna I. Krylov

J. Chem. Phys. 138, 124106 (2013); http://dx.doi.org/10.1063/1.4795750 (15 pages)

Online Publication Date: 26 March 2013

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Theory and implementation of complex-scaled variant of equation-of-motion coupled-cluster method for excitation energies with single and double substitutions (EOM-EE-CCSD) is presented. The complex-scaling formalism extends the EOM-EE-CCSD model to resonance states, i.e., excited states that are metastable with respect to electron ejection. The method is applied to Feshbach resonances in atomic systems (He, H−, and Be). The dependence of the results on one-electron basis set is quantified and analyzed. Energy decomposition and wave function analysis reveal that the origin of the dependence is in electron correlation, which is essential for the lifetime of Feshbach resonances. It is found that one-electron basis should be sufficiently flexible to describe radial and angular electron correlation in a balanced fashion and at different values of the scaling parameter, θ. Standard basis sets that are optimized for not-complex-scaled calculations (θ = 0) are not sufficiently flexible to describe the θ-dependence of the wave functions even when heavily augmented by additional sets.
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31.15.bw Coupled-cluster theory
31.15.vj Electron correlation calculations for atoms and ions: excited states
32.80.Zb Autoionization

Double excitations from modified Hartree Fock subsequent minimization scheme

M. Tassi, Iris Theophilou, and S. Thanos

J. Chem. Phys. 138, 124107 (2013); http://dx.doi.org/10.1063/1.4797466 (8 pages)

Online Publication Date: 27 March 2013

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Doubly excited states have nowadays become important in technological applications, e.g., in increasing the efficiency of solar cells and therefore, their description using ab initio methods is a great theoretical challenge as double excitations cannot be described by linear response theories based on a single Slater determinant. In the present work we extend our recently developed Hartree-Fock (HF) approximation for calculating singly excited states [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013)10.1002/qua.24049] in order to allow for the calculation of doubly excited states. We describe the double excitation as two holes in the subspace spanned from the occupied HF orbitals and two particles in the subspace of virtual HF orbitals. A subsequent minimization of the energy results to the determination of the spin orbitals of both the holes and the particles in the occupied and virtual subspaces, respectively. We test our method, for various atoms, H2 and polyene molecules which are known to have excitations presenting a significant double excitation character. Importantly, our approach is computationally inexpensive.
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31.15.xr Self-consistent-field methods
31.15.ag Excitation energies and lifetimes; oscillator strengths

Nonadiabatic anharmonic electron transfer

P. P. Schmidt

J. Chem. Phys. 138, 124108 (2013); http://dx.doi.org/10.1063/1.4795581 (16 pages)

Online Publication Date: 27 March 2013

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The effect of an inner sphere, local mode vibration on an electron transfer is modeled using the nonadiabatic transition probability (rate) expression together with both the anharmonic Morse and the harmonic oscillator potential. For an anharmonic inner sphere mode, a variational analysis uses harmonic oscillator basis functions to overcome the difficulties evaluating Morse-model Franck-Condon overlap factors. Individual matrix elements are computed with the use of new, fast, robust, and flexible recurrence relations. The analysis therefore readily addresses changes in frequency and/or displacement of oscillator minimums in the different electron transfer states. Direct summation of the individual Boltzmann weighted Franck-Condon contributions avoids the limitations inherent in the use of the familiar high-temperature, Gaussian form of the rate constant. The effect of harmonic versus anharmonic inner sphere modes on the electron transfer is readily seen, especially in the exoergic, inverted region. The behavior of the transition probability can also be displayed as a surface for all temperatures and values of the driving force/exoergicity Δ = −ΔG. The temperature insensitivity of the transfer rate is clearly seen when the exoergicity equals the collective reorganization energy (Δ = Λs) along a maximum ln (w) vs. Δ ridge of the surface. The surface also reveals additional regions for Δ where ln (w) appears to be insensitive to temperature, or effectively activationless, for some kinds of inner sphere contributions.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
82.20.Db Transition state theory and statistical theories of rate constants

A combined quasi-continuum/Langevin equation approach to study the self-diffusion dynamics of confined fluids

T. Sanghi and N. R. Aluru

J. Chem. Phys. 138, 124109 (2013); http://dx.doi.org/10.1063/1.4796387 (9 pages)

Online Publication Date: 28 March 2013

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In this work, we combine our earlier proposed empirical potential based quasi-continuum theory, (EQT) [A. V. Raghunathan, J. H. Park, and N. R. Aluru, J. Chem. Phys. 127, 174701 (2007)10.1063/1.2793070], which is a coarse-grained multiscale framework to predict the static structure of confined fluids, with a phenomenological Langevin equation to simulate the dynamics of confined fluids in thermal equilibrium. An attractive feature of this approach is that all the input parameters to the Langevin equation (mean force profile of the confined fluid and the static friction coefficient) can be determined using the outputs of the EQT and the self-diffusivity data of the corresponding bulk fluid. The potential of mean force profile, which is a direct output from EQT is used to compute the mean force profile of the confined fluid. The density profile, which is also a direct output from EQT, along with the self-diffusivity data of the bulk fluid is used to determine the static friction coefficient of the confined fluid. We use this approach to compute the mean square displacement and survival probabilities of some important fluids such as carbon-dioxide, water, and Lennard-Jones argon confined inside slit pores. The predictions from the model are compared with those obtained using molecular dynamics simulations. This approach of combining EQT with a phenomenological Langevin equation provides a mathematically simple and computationally efficient means to study the impact of structural inhomogeneity on the self-diffusion dynamics of confined fluids.
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66.10.cg Mass diffusion, including self-diffusion, mutual diffusion, tracer diffusion, etc.
02.50.Cw Probability theory
62.10.+s Mechanical properties of liquids
61.20.Ja Computer simulation of liquid structure

Spin-adaptation and redundancy in state-specific multireference perturbation theory

Péter Jeszenszki, Péter R. Surján, and Ágnes Szabados

J. Chem. Phys. 138, 124110 (2013); http://dx.doi.org/10.1063/1.4795436 (14 pages)

Online Publication Date: 28 March 2013

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Spin-adaptation of virtual functions in state-specific multireference perturbation theory is examined. Redundancy occurring among virtual functions generated by unitary group based excitation operators on a model-space function is handled by canonical orthogonalization. The treatment is found to remove non-physical kinks observed earlier on potential energy surfaces. Sensitivity analysis of the new approach confirms the elimination of the drastic increase in singular values of sensitivity matrices, reported earlier.
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31.15.xp Perturbation theory
31.50.-x Potential energy surfaces

Quartic scaling second-order approximate coupled cluster singles and doubles via tensor hypercontraction: THC-CC2

Edward G. Hohenstein, Sara I. L. Kokkila, Robert M. Parrish, and Todd J. Martínez

J. Chem. Phys. 138, 124111 (2013); http://dx.doi.org/10.1063/1.4795514 (10 pages)

Online Publication Date: 28 March 2013

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The second-order approximate coupled cluster singles and doubles method (CC2) is a valuable tool in electronic structure theory. Although the density fitting approximation has been successful in extending CC2 to larger molecules, it cannot address the steep O(N5) scaling with the number of basis functions, N. Here, we introduce the tensor hypercontraction (THC) approximation to CC2 (THC-CC2), which reduces the scaling to O(N4) and the storage requirements to O(N2). We present an algorithm to efficiently evaluate the THC-CC2 correlation energy and demonstrate its quartic scaling. This implementation of THC-CC2 uses a grid-based least-squares THC (LS-THC) approximation to the density-fitted electron repulsion integrals. The accuracy of the CC2 correlation energy under these approximations is shown to be suitable for most practical applications.
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31.15.bw Coupled-cluster theory
31.15.eg Exchange-correlation functionals (in current density functional theory)

Semilocal and hybrid density embedding calculations of ground-state charge-transfer complexes

S. Laricchia, E. Fabiano, and F. Della Sala

J. Chem. Phys. 138, 124112 (2013); http://dx.doi.org/10.1063/1.4795825 (12 pages)

Online Publication Date: 28 March 2013

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We apply the frozen density embedding method, using a full relaxation of embedded densities through a freeze-and-thaw procedure, to study the electronic structure of several benchmark ground-state charge-transfer complexes, in order to assess the merits and limitations of the approach for this class of systems. The calculations are performed using both semilocal and hybrid exchange-correlation (XC) functionals. The results show that embedding calculations using semilocal XC functionals yield rather large deviations with respect to the corresponding supermolecular calculations. Due to a large error cancellation effect, however, they can often provide a relatively good description of the electronic structure of charge-transfer complexes, in contrast to supermolecular calculations performed at the same level of theory. On the contrary, when hybrid XC functionals are employed, both embedding and supermolecular calculations agree very well with each other and with the reference benchmark results. In conclusion, for the study of ground-state charge-transfer complexes via embedding calculations hybrid XC functionals are the method of choice due to their higher reliability and superior performance.
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34.70.+e Charge transfer
31.15.eg Exchange-correlation functionals (in current density functional theory)

Accurate prediction of nuclear magnetic resonance shielding constants: Towards the accuracy of CCSD(T) complete basis set limit

Meng Sun, Igor Ying Zhang, Anan Wu, and Xin Xu

J. Chem. Phys. 138, 124113 (2013); http://dx.doi.org/10.1063/1.4796485 (9 pages)

Online Publication Date: 29 March 2013

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In this work, we have calculated the nuclear magnetic resonance (NMR) shielding constants for 42 molecules at the levels of second order Møller-Plesset perturbation (MP2) and coupled-cluster singles and doubles model augmented by perturbative corrections for triple excitations CCSD(T). Basis set extrapolations to the complete basis set (CBS) limit have been performed. A focal-point analysis method for magnetic parameters was proposed here, which adds the [σe(CCSD(T)) − σe(MP2)] difference to the MP2/CBS number to approximate the corresponding CCSD(T)/CBS value. Systematical comparison has demonstrated the usefulness of this FPA-M/CBS scheme.
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31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory
33.25.+k Nuclear resonance and relaxation

Topology of classical molecular optimal control landscapes in phase space

Carlee Joe-Wong, Tak-San Ho, Ruixing Long, Herschel Rabitz, and Rebing Wu

J. Chem. Phys. 138, 124114 (2013); http://dx.doi.org/10.1063/1.4797498 (15 pages)

Online Publication Date: 29 March 2013

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Optimal control of molecular dynamics is commonly expressed from a quantum mechanical perspective. However, in most contexts the preponderance of molecular dynamics studies utilize classical mechanical models. This paper treats laser-driven optimal control of molecular dynamics in a classical framework. We consider the objective of steering a molecular system from an initial point in phase space to a target point, subject to the dynamic constraint of Hamilton's equations. The classical control landscape corresponding to this objective is a functional of the control field, and the topology of the landscape is analyzed through its gradient and Hessian with respect to the control. Under specific assumptions on the regularity of the control fields, the classical control landscape is found to be free of traps that could hinder reaching the objective. The Hessian associated with an optimal control field is shown to have finite rank, indicating the presence of an inherent degree of robustness to control noise. Extensive numerical simulations are performed to illustrate the theoretical principles on (a) a model diatomic molecule, (b) two coupled Morse oscillators, and (c) a chaotic system with a coupled quartic oscillator, confirming the absence of traps in the classical control landscape. We compare the classical formulation with the mathematically analogous quantum state-to-state transition probability control landscape.
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33.80.-b Photon interactions with molecules
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
03.65.-w Quantum mechanics
back to top Atoms, Molecules, and Clusters
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Vibrational and electronic excitations in fluorinated ethene cations from the ground up

Jonelle Harvey, Patrick Hemberger, Andras Bodi, and Richard P. Tuckett

J. Chem. Phys. 138, 124301 (2013); http://dx.doi.org/10.1063/1.4795428 (12 pages)

Online Publication Date: 22 March 2013

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Valence threshold photoelectron spectra of four fluorinated ethenes; C2H3F, 1,1-C2H2F2, C2HF3, and C2F4 were recorded at the Swiss Light Source with 0.002 eV resolution. The adiabatic ionization energies were found to be 10.364 ± 0.007, 10.303 ± 0.005, 10.138 ± 0.007, and 10.110 ± 0.009 eV, respectively. The electronic ground state of each cation shows well-resolved multi-component vibrational progressions, the dominant transitions being in the C=C stretching mode. Density functional theory based Franck–Condon simulations are used to model the vibrational structure and assign the spectra, sometimes revising previous assignments. An additional vibrational progression in the first photoelectron band of 1,1-C2H2F2 indicates that the ground electronic state of the molecular ion is no longer planar. It is shown that ab initio vibrational frequencies together with the observed vibrational spacings do not always suffice to assign the spectra. In addition to symmetry rules governing the transitions, it is often essential to consider the associated Franck–Condon factors explicitly. Ionization to higher lying excited valence electronic states were also recorded by threshold ionization up to 23 eV photon energy. Equation-of-motion coupled cluster with single and double substitutions for ionization potential (EOM-IP-CCSD/cc-pVTZ) calculations confirmed historic electronic state assignments, and untangled the ever more congested spectra with increasing F-substitution. Previous attempts at illuminating the intriguing dissociative photoionization mechanism of fluorinated ethenes are reconsidered in view of new computational and experimental results. We show how non-statistical F-atom loss from C2H3F+ is decoupled from the ground state dissociation dynamics in the energy range of its math state. Both the statistical and the non-statistical dissociation processes are mediated by a plethora of conical intersections.
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33.20.Tp Vibrational analysis
33.80.Gj Diffuse spectra; predissociation, photodissociation
31.15.ae Electronic structure and bonding characteristics
31.15.E- Density-functional theory
33.60.+q Photoelectron spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

Ab initio studies of atomic properties and experimental behavior of element 119 and its lighter homologs

A. Borschevsky, V. Pershina, E. Eliav, and U. Kaldor

J. Chem. Phys. 138, 124302 (2013); http://dx.doi.org/10.1063/1.4795433 (5 pages)

Online Publication Date: 22 March 2013

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Static dipole polarizabilities of element 119 and its singly charged cation are calculated, along with those of its lighter homologs, Cs and Fr. Relativity is treated within the 4-component Dirac-Coulomb formalism and electron correlation is included by the single reference coupled cluster approach with single, double, and perturbative triple excitations (CCSD(T)). Very good agreement with available experimental values is obtained for Cs, lending credence to the predictions for Fr and element 119. The atomic properties in group-1 are largely determined by the valence ns orbital, which experiences relativistic stabilization and contraction in the heavier elements. As a result, element 119 is predicted to have a relatively low polarizability (169.7 a.u.), comparable to that of Na. The adsorption enthalpy of element 119 on Teflon, which is important for possible future experimental studies of this element, is estimated as 17.6 kJ/mol, the lowest among the atoms considered here.
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31.15.ap Polarizabilities and other atomic and molecular properties
31.15.bw Coupled-cluster theory
31.15.vj Electron correlation calculations for atoms and ions: excited states
31.30.jc Relativistic corrections to atomic structure and properties
32.30.-r Atomic spectra
68.43.Mn Adsorption kinetics

Photoelectron spectroscopy of the aluminum hydride anions: AlH2−, AlH3−, Al2H6−, Al3H9−, and Al4H12−

Xinxing Zhang, Haopeng Wang, Evan Collins, Alane Lim, Gerd Ganteför, Boggavarapu Kiran, Hansgeorg Schnöckel, Bryan Eichhorn, and Kit Bowen

J. Chem. Phys. 138, 124303 (2013); http://dx.doi.org/10.1063/1.4796200 (4 pages)

Online Publication Date: 25 March 2013

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We report measurements of the negative ion photoelectron spectra of the simple aluminum hydride anions: AlH2−, AlH3−, Al2H6−, Al3H9−, and Al4H12−. From these spectra, we measured the vertical detachment energies of the anions, and we estimated the electron affinities of their neutral counterparts. Our results for AlH2−, AlH3−, and Al2H6− were also compared with previous predictions by theory.
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33.60.+q Photoelectron spectra
33.20.Xx Spectra induced by strong-field or attosecond laser irradiation
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Fm Bond strengths, dissociation energies

Ion imaging study of dissociative charge transfer in the N2+ + CH4 system

Linsen Pei and James M. Farrar

J. Chem. Phys. 138, 124304 (2013); http://dx.doi.org/10.1063/1.4796205 (5 pages)

Online Publication Date: 25 March 2013

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The velocity map ion imaging method is applied to the dissociative charge transfer reactions of N2+ with CH4 studied in crossed beams. The velocity space images are collected at four collision energies between 0.5 and 1.5 eV, providing both product kinetic energy and angular distributions for the reaction products CH3+ and CH2+. The general shapes of the images are consistent with long range electron transfer from CH4 to N2+ preceding dissociation, and product kinetic energy distributions are consistent with energy resonance in the initial electron transfer step. The branching ratio for CH3+:CH2+ is 85:15 over the full collision energy range, consistent with literature reports.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
34.70.+e Charge transfer
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Vibrational Raman spectra of hydrogen clathrate hydrates from density functional theory

K. R. Ramya and Arun Venkatnathan

J. Chem. Phys. 138, 124305 (2013); http://dx.doi.org/10.1063/1.4795610 (6 pages)

Online Publication Date: 25 March 2013

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Hydrogen clathrate hydrates are promising sources of clean energy and are known to exist in a sII hydrate lattice, which consists of H2 molecules in dodecahedron (512) and hexakaidecahedron (51264) water cages. The formation of these hydrates which occur in extreme thermodynamic conditions is known to be considerably reduced by an inclusion of tetrahydrofuran (THF) in cages of these hydrate lattice. In this present work, we employ the density functional theory with a dispersion corrected (B97-D) functional to characterize vibrational Raman modes in the cages of pure and THF doped hydrogen clathrate hydrates. Our calculations show that the symmetric stretch of the H2 molecule in the 51264H2·THF cage is blueshifted compared to the 51264H2 cage. However, all vibrational modes of water molecules are redshifted which suggest reduced interaction between the H2 molecule and water molecules in the 51264H2·THF cage. The symmetric and asymmetric O–H stretch of water molecules in 512H2, 51264H2, and 51264H2·THF cages are redshifted compared with the corresponding guest free cages due to interactions between encapsulated H2 molecules and water molecules of the cages. The low frequency modes contain contributions from contraction and expansion of water cages and vibration of water molecules due to hydrogen bonding and these modes could possibly play an important role in the formation of the hydrate lattice.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
65.40.G- Other thermodynamical quantities
61.50.Lt Crystal binding; cohesive energy
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.30.Jw Organic compounds, polymers
63.50.-x Vibrational states in disordered systems

Ionization of large homogeneous and heterogeneous clusters generated in acetylene–Ar expansions: Cluster ion polymerization

J. Kočišek, J. Lengyel, and M. Fárník

J. Chem. Phys. 138, 124306 (2013); http://dx.doi.org/10.1063/1.4796262 (8 pages)

Online Publication Date: 26 March 2013

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Pure acetylene and mixed Ar-acetylene clusters are formed in supersonic expansions of acetylene/argon mixtures and analysed using reflectron time-of-flight mass spectrometer with variable electron energy ionization source. Acetylene clusters composed of more than a hundred acetylene molecules are generated at the acetylene concentration of ≈8%, while mixed species are produced at low concentrations (≈0.7%). The electron energy dependence of the mass spectra revealed the ionization process mechanisms in clusters. The ionization above the threshold for acetylene molecule of 11.5 eV results in the main ionic fragment progression (C2H2)n+. At the electron energies ⩾21.5 eV above the CH+CH+ dissociative ionization limit of acetylene the fragment ions nominally labelled as (C2H2)nCH+, n ⩾ 2, are observed. For n ⩽ 7 these fragments correspond to covalently bound ionic structures as suggested by the observed strong dehydrogenation [(C2H2)n − k × H]+ and [(C2H2)nCH − k × H]+. The dehydrogenation is significantly reduced in the mixed clusters where evaporation of Ar instead of hydrogen can stabilize the nascent molecular ion. The C3H3+ ion was previously assigned to originate from the benzene molecular ion; however, the low appearance energy of ≈13.7 eV indicates that a less rigid covalently bound structure of C6H6+ ion must also be formed upon the acetylene cluster electron ionization. The appearance energy of Arn(C2H2)+ fragments above ≈15.1 eV indicates that the argon ionization is the first step in the fragment ion production, and the appearance energy of Ar n ≥ 2(C2H2)m ≥ 2+ at ≈13.7 eV is discussed in terms of an exciton transfer mechanism.
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36.40.Jn Reactivity of clusters
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
34.80.Gs Molecular excitation and ionization
33.15.Ta Mass spectra
36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Qv Stability and fragmentation of clusters

Morphology of collisional nonlinear spectra in H2-Kr and H2-Xe mixtures

Waldemar Głaz, Tadeusz Bancewicz, Jean-Luc Godet, George Maroulis, and Anastasios Haskopoulos

J. Chem. Phys. 138, 124307 (2013); http://dx.doi.org/10.1063/1.4795438 (7 pages)

Online Publication Date: 26 March 2013

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This article reports new results of theoretical and numerical studies of spectral features of the collision-induced hyper-Rayleigh light scattered in dihydrogen-noble gas (H2-Rg) mixtures. The most massive and polarizable scattering supermolecules with Rg = Kr and Xe have been added to the previously considered systems in order to gain a more complete insight into the evolution of the spectral properties. The symmetry adapted components of the first collisional hyperpolarizabilities are obtained by means of the quantum chemistry numerical routines supplemented with appropriate theoretical methods. Roto-translational spectral lines are calculated on the grounds of the quantum-mechanical as well as semi-classical approach. The role of particular hyperpolarizability components in forming the line shapes is discussed. The intensities of the lines are compared with those obtained for less massive scatterers. Advantages of prospective application of the new scattering systems for experimental detection of the nonlinear collisional effects are indicated.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.70.Fd Absolute and relative line and band intensities
33.70.Jg Line and band widths, shapes, and shifts
34.50.-s Scattering of atoms and molecules
31.15.xv Molecular dynamics and other numerical methods
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

High temperature reaction kinetics of CN(v = 0) with C2H4 and C2H6 and vibrational relaxation of CN(v = 1) with Ar and He

Ghassen Saidani, Yulia Kalugina, Aline Gardez, Ludovic Biennier, Robert Georges, and François Lique

J. Chem. Phys. 138, 124308 (2013); http://dx.doi.org/10.1063/1.4795206 (13 pages)

Online Publication Date: 27 March 2013

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The investigation of the chemical complexity of hot environments, ranging from combustion flames to circumstellar envelopes of evolved stars, relies on the determination of the reaction kinetics and product branching ratio. We have designed a chemical reactor for the exploration of high temperature chemistry. This apparatus is employed in the present study to measure the reaction kinetics of the CN radical with C2H4 and C2H6 over the 300–1200 K temperature range. In our setup and in some environments, the CN radical is partially produced in a vibrationally excited state, before relaxing by collision with the surrounding gas. We complement the experimental kinetic studies of hydrocarbons reactions with CN(v = 0) with a theoretical study of vibrational relaxation of CN(v = 1) by He and Ar atoms, the main collisional partners in our apparatus. Calculations are carried out to determine the collisional elastic and inelastic cross sections versus the kinetic energy as well as the corresponding vibrationally elastic and inelastic rate coefficients. The results are compared with empirical calculations and with a few experimental observations. The range of validity of the empirical model is discussed and potential applications sketched.
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82.20.Rp State to state energy transfer
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.33.Vx Reactions in flames, combustion, and explosions
33.15.Mt Rotation, vibration, and vibration-rotation constants
34.50.Ez Rotational and vibrational energy transfer

Full-dimensional quantum calculations of the vibrational states of H5+

Hongwei Song, Soo-Ying Lee, Minghui Yang, and Yunpeng Lu

J. Chem. Phys. 138, 124309 (2013); http://dx.doi.org/10.1063/1.4797464 (10 pages)

Online Publication Date: 28 March 2013

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Full-dimensional quantum calculations of the vibrational states of H5+ have been performed on the accurate potential energy surface developed by Xie et al. [J. Chem. Phys. 122, 224307 (2005)10.1063/1.1927529]. The zero point energies of H5+, H4D+, D4H+, and D5+ and their ground-state geometries are presented and compared with earlier theoretical results. The first 10 low-lying excited states of H5+ are assigned to the fundamental, overtone, and combination of the H2–H3+ stretch, the shared proton hopping and the out-of-plane torsion. The ground-state torsional tunneling splitting, the fundamental of the photon hopping mode and the first overtone of the torsion mode are 87.3 cm −1, 354.4 cm −1, and 444.0 cm −1, respectively. All of these values agree well with the diffusion Monte Carlo and multi-configuration time-dependent Hartree results where available.
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33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.xr Self-consistent-field methods
31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states

Resonance Regge poles and the state-to-state F + H2 reaction: QP decomposition, parametrized S matrix, and semiclassical complex angular momentum analysis of the angular scattering

J. N. L. Connor

J. Chem. Phys. 138, 124310 (2013); http://dx.doi.org/10.1063/1.4794859 (21 pages)

Online Publication Date: 28 March 2013

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Three new contributions to the complex angular momentum (CAM) theory of differential cross sections (DCSs) for chemical reactions are reported. They exploit recent advances in the Padé reconstruction of a scattering (S) matrix in a region surrounding the Re J axis, where J is the total angular momentum quantum variable, starting from the discrete values, J = 0, 1, 2, …. In particular, use is made of Padé continuations obtained by Sokolovski, Castillo, and Tully [Chem. Phys. Lett. 313, 225 (1999)10.1016/S0009-2614(99)01016-7] for the S matrix of the benchmark F + H2(vi = 0, ji = 0, mi = 0) → FH(vf = 3, jf = 3, mf = 0) + H reaction. Here vi, ji, mi and vf, jf, mf are the initial and final vibrational, rotational, and helicity quantum numbers, respectively. The three contributions are: (1) A new exact decomposition of the partial wave (PW) S matrix is introduced, which is called the QP decomposition. The P part contains information on the Regge poles. The Q part is then constructed exactly by subtracting a rapidly oscillating phase and the PW P matrix from the input PW S matrix. After a simple modification, it is found that the corresponding scattering subamplitudes provide insight into the angular-scattering dynamics using simple partial wave series (PWS) computations. It is shown that the leading n = 0 Regge pole contributes to the small-angle scattering in the centre-of-mass frame. (2) The Q matrix part of the QP decomposition has simpler properties than the input S matrix. This fact is exploited to deduce a parametrized (analytic) formula for the PW S matrix in which all terms have a direct physical interpretation. This is a long sort-after goal in reaction dynamics, and in particular for the state-to-state F + H2 reaction. (3) The first definitive test is reported for the accuracy of a uniform semiclassical (asymptotic) CAM theory for a DCS based on the Watson transformation. The parametrized S matrix obtained in contribution (2) is used in both the PW and semiclassical parts of the calculation. Powerful uniform asymptotic approximations are employed for the background integral; they allow for the proximity of a Regge pole and a saddle point. The CAM DCS agrees well with the PWS DCS, across the whole angular range, except close to the forward and backward directions, where, as expected, the CAM theory becomes non-uniform. At small angles, θR ≲ 40°, the PWS DCS can be reproduced using a nearside semiclassical subamplitude, which allows for a pole being close to a saddle point, plus the farside surface wave of the n = 0 pole sub-subamplitude, with the oscillations in the DCS arising from nearside-farside interference. This proves that the n = 0 Regge resonance pole contributes to the small-angle scattering.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Ln Semiclassical theory of reactions and/or energy transfer
33.20.Tp Vibrational analysis
33.20.Sn Rotational analysis

Carbon X-ray absorption spectra of fluoroethenes and acetone: A study at the coupled cluster, density functional, and static-exchange levels of theory

Thomas Fransson, Sonia Coriani, Ove Christiansen, and Patrick Norman

J. Chem. Phys. 138, 124311 (2013); http://dx.doi.org/10.1063/1.4795835 (12 pages)

Online Publication Date: 29 March 2013

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Near carbon K-edge X-ray absorption fine structure spectra of a series of fluorine-substituted ethenes and acetone have been studied using coupled cluster and density functional theory (DFT) polarization propagator methods, as well as the static-exchange (STEX) approach. With the complex polarization propagator (CPP) implemented in coupled cluster theory, relaxation effects following the excitation of core electrons are accounted for in terms of electron correlation, enabling a systematic convergence of these effects with respect to electron excitations in the cluster operator. Coupled cluster results have been used as benchmarks for the assessment of propagator methods in DFT as well as the state-specific static-exchange approach. Calculations on ethene and 1,1-difluoroethene illustrate the possibility of using nonrelativistic coupled cluster singles and doubles (CCSD) with additional effects of electron correlation and relativity added as scalar shifts in energetics. It has been demonstrated that CPP spectra obtained with coupled cluster singles and approximate doubles (CC2), CCSD, and DFT (with a Coulomb attenuated exchange-correlation functional) yield excellent predictions of chemical shifts for vinylfluoride, 1,1-difluoroethene, trifluoroethene, as well as good spectral features for acetone in the case of CCSD and DFT. Following this, CPP-DFT is considered to be a viable option for the calculation of X-ray absorption spectra of larger π-conjugated systems, and CC2 is deemed applicable for chemical shifts but not for studies of fine structure features. The CCSD method as well as the more approximate CC2 method are shown to yield spectral features relating to π*-resonances in good agreement with experiment, not only for the aforementioned molecules but also for ethene, cis-1,2-difluoroethene, and tetrafluoroethene. The STEX approach is shown to underestimate π*-peak separations due to spectral compressions, a characteristic which is inherent to this method.
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33.20.Rm X-ray spectra
31.15.E- Density-functional theory
31.15.bw Coupled-cluster theory
31.15.eg Exchange-correlation functionals (in current density functional theory)
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